Next waypoint ETA calculator

The next waypoint ETA calculator turns one navigation fix into a practical progress estimate. Supply the current latitude and longitude, the next waypoint coordinates, the bearing followed on the active route leg, and present speed. It measures the great-circle distance still separating the two positions, finds the initial bearing toward the waypoint, compares that direction with the route bearing, and uses only the speed component that is actually closing the gap. The result includes remaining distance, course error, closing speed, ETA in seconds and minutes, and a readable duration. It runs deterministically without live maps, traffic, weather, network requests, or the current clock.

What the waypoint estimate measures

A waypoint ETA is most useful when it describes progress on the leg you are following, rather than dividing straight-line distance by the full speed regardless of direction. This calculator begins with the current position and next waypoint as decimal-degree coordinates. It calculates their shortest surface separation on a sphere using the haversine formula and the IUGG mean Earth radius.

It then calculates the initial true bearing from the current fix to the waypoint. The tool projects speed onto the waypoint direction with the cosine of that error. A vessel, aircraft, cyclist, or other moving object aimed directly at the waypoint therefore uses its full speed; one travelling obliquely has a lower closing speed and a longer ETA.

The method is an instantaneous estimate from one fix, not a forecast of future turns or speed changes. If the current position is already at the waypoint, distance and ETA are zero.

How to enter a route fix and interpret the result

Latitudes accept negative values south of the equator and positive values north of it, while longitudes are negative west of Greenwich and positive east of it. Coordinates are range-checked, and longitude differences are wrapped across the antimeridian so a short leg near 180 degrees does not accidentally become an almost complete trip around Earth. The speed field must be strictly positive.

Precision controls zero through nine decimal places for numeric output without altering the underlying calculation. ETA is distance divided by closing speed, not by total speed. For example, a 60-degree course error leaves only half of the current speed closing the waypoint, so the instantaneous ETA is approximately twice the direct-heading estimate.

Limits of an instantaneous ETA and good operational use

Treat this output as a transparent snapshot, not as turn-by-turn navigation or a promise of arrival. The estimate assumes the current bearing and speed continue while the remaining great-circle separation closes. It does not know the geometry of later route segments, restricted areas, currents, wind, traffic, climb profiles, terrain, scheduled stops, or acceleration.

It also uses a spherical Earth rather than an ellipsoidal geodesic, an appropriate trade-off for quick leg monitoring and repeatable automation but not a substitute for certified navigation equipment. On a curved or deliberately offset route, update the calculation after each position fix so course error and closing speed reflect the newest motion. If your route mandates following a polyline rather than moving toward the waypoint, compute the remaining polyline length elsewhere; this capability measures current-to-waypoint surface distance and adjusts time for the supplied heading.

The explicit rejection of a non-closing bearing is operationally valuable: it can flag a reversed course, a stale waypoint, swapped coordinates, or a vehicle moving along a holding pattern before downstream software displays a plausible-looking arrival. For noisy GPS feeds, smooth position, bearing, and speed before calling the solver, or require several consistent fixes before acting on an ETA change. No input is stored by the solver, no live location is fetched, and no system time is consulted.